From: David Hildenbrand <david@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, "David Hildenbrand" <david@redhat.com>,
"Michal Hocko" <mhocko@kernel.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
kvm@vger.kernel.org, linux-hyperv@vger.kernel.org,
devel@driverdev.osuosl.org, xen-devel@lists.xenproject.org,
x86@kernel.org, "Alexander Duyck" <alexander.duyck@gmail.com>,
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YueHaibing <yuehaibing@huawei.com>
Subject: [PATCH RFC v1 00/12] mm: Don't mark hotplugged pages PG_reserved (including ZONE_DEVICE)
Date: Tue, 22 Oct 2019 19:12:27 +0200 [thread overview]
Message-ID: <20191022171239.21487-1-david@redhat.com> (raw)
This series is based on [2], which should pop up in linux/next soon:
https://lkml.org/lkml/2019/10/21/1034
This is the result of a recent discussion with Michal ([1], [2]). Right
now we set all pages PG_reserved when initializing hotplugged memmaps. This
includes ZONE_DEVICE memory. In case of system memory, PG_reserved is
cleared again when onlining the memory, in case of ZONE_DEVICE memory
never. In ancient times, we needed PG_reserved, because there was no way
to tell whether the memmap was already properly initialized. We now have
SECTION_IS_ONLINE for that in the case of !ZONE_DEVICE memory. ZONE_DEVICE
memory is already initialized deferred, and there shouldn't be a visible
change in that regard.
I remember that some time ago, we already talked about stopping to set
ZONE_DEVICE pages PG_reserved on the list, but I never saw any patches.
Also, I forgot who was part of the discussion :)
One of the biggest fear were side effects. I went ahead and audited all
users of PageReserved(). The ones that don't need any care (patches)
can be found below. I will double check and hope I am not missing something
important.
I am probably a little bit too careful (but I don't want to break things).
In most places (besides KVM and vfio that are nuts), the
pfn_to_online_page() check could most probably be avoided by a
is_zone_device_page() check. However, I usually get suspicious when I see
a pfn_valid() check (especially after I learned that people mmap parts of
/dev/mem into user space, including memory without memmaps. Also, people
could memmap offline memory blocks this way :/). As long as this does not
hurt performance, I think we should rather do it the clean way.
I only gave it a quick test with DIMMs on x86-64, but didn't test the
ZONE_DEVICE part at all (any tips for a nice QEMU setup?). Compile-tested
on x86-64 and PPC.
Other users of PageReserved() that should be fine:
- mm/page_owner.c:pagetypeinfo_showmixedcount_print()
-> Never called for ZONE_DEVICE, (+ pfn_to_online_page(pfn))
- mm/page_owner.c:init_pages_in_zone()
-> Never called for ZONE_DEVICE (!populated_zone(zone))
- mm/page_ext.c:free_page_ext()
-> Only a BUG_ON(PageReserved(page)), not relevant
- mm/page_ext.c:has_unmovable_pages()
-> Not releveant for ZONE_DEVICE
- mm/page_ext.c:pfn_range_valid_contig()
-> pfn_to_online_page() already guards us
- mm/mempolicy.c:queue_pages_pte_range()
-> vm_normal_page() checks against pte_devmap()
- mm/memory-failure.c:hwpoison_user_mappings()
-> Not reached via memory_failure() due to pfn_to_online_page()
-> Also not reached indirectly via memory_failure_hugetlb()
- mm/hugetlb.c:gather_bootmem_prealloc()
-> Only a WARN_ON(PageReserved(page)), not relevant
- kernel/power/snapshot.c:saveable_highmem_page()
-> pfn_to_online_page() already guards us
- kernel/power/snapshot.c:saveable_page()
-> pfn_to_online_page() already guards us
- fs/proc/task_mmu.c:can_gather_numa_stats()
-> vm_normal_page() checks against pte_devmap()
- fs/proc/task_mmu.c:can_gather_numa_stats_pmd
-> vm_normal_page_pmd() checks against pte_devmap()
- fs/proc/page.c:stable_page_flags()
-> The reserved bit is simply copied, irrelevant
- drivers/firmware/memmap.c:release_firmware_map_entry()
-> really only a check to detect bootmem. Not relevant for ZONE_DEVICE
- arch/ia64/kernel/mca_drv.c
- arch/mips/mm/init.c
- arch/mips/mm/ioremap.c
- arch/nios2/mm/ioremap.c
- arch/parisc/mm/ioremap.c
- arch/sparc/mm/tlb.c
- arch/xtensa/mm/cache.c
-> No ZONE_DEVICE support
- arch/powerpc/mm/init_64.c:vmemmap_free()
-> Special-cases memmap on altmap
-> Only a check for bootmem
- arch/x86/kernel/alternative.c:__text_poke()
-> Only a WARN_ON(!PageReserved(pages[0])) to verify it is bootmem
- arch/x86/mm/init_64.c
-> Only a check for bootmem
[1] https://lkml.org/lkml/2019/10/21/736
[2] https://lkml.org/lkml/2019/10/21/1034
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: kvm-ppc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: kvm@vger.kernel.org
Cc: linux-hyperv@vger.kernel.org
Cc: devel@driverdev.osuosl.org
Cc: xen-devel@lists.xenproject.org
Cc: x86@kernel.org
Cc: Alexander Duyck <alexander.duyck@gmail.com>
David Hildenbrand (12):
mm/memory_hotplug: Don't allow to online/offline memory blocks with
holes
mm/usercopy.c: Prepare check_page_span() for PG_reserved changes
KVM: x86/mmu: Prepare kvm_is_mmio_pfn() for PG_reserved changes
KVM: Prepare kvm_is_reserved_pfn() for PG_reserved changes
vfio/type1: Prepare is_invalid_reserved_pfn() for PG_reserved changes
staging/gasket: Prepare gasket_release_page() for PG_reserved changes
staging: kpc2000: Prepare transfer_complete_cb() for PG_reserved
changes
powerpc/book3s: Prepare kvmppc_book3s_instantiate_page() for
PG_reserved changes
powerpc/64s: Prepare hash_page_do_lazy_icache() for PG_reserved
changes
powerpc/mm: Prepare maybe_pte_to_page() for PG_reserved changes
x86/mm: Prepare __ioremap_check_ram() for PG_reserved changes
mm/memory_hotplug: Don't mark pages PG_reserved when initializing the
memmap
arch/powerpc/kvm/book3s_64_mmu_radix.c | 14 ++++---
arch/powerpc/mm/book3s64/hash_utils.c | 10 +++--
arch/powerpc/mm/pgtable.c | 10 +++--
arch/x86/kvm/mmu.c | 30 +++++++++------
arch/x86/mm/ioremap.c | 13 +++++--
drivers/hv/hv_balloon.c | 6 +++
drivers/staging/gasket/gasket_page_table.c | 2 +-
drivers/staging/kpc2000/kpc_dma/fileops.c | 3 +-
drivers/vfio/vfio_iommu_type1.c | 10 ++++-
drivers/xen/balloon.c | 7 ++++
include/linux/page-flags.h | 8 +---
mm/memory_hotplug.c | 43 ++++++++++++++++------
mm/page_alloc.c | 11 ------
mm/usercopy.c | 5 ++-
virt/kvm/kvm_main.c | 10 ++++-
15 files changed, 115 insertions(+), 67 deletions(-)
--
2.21.0
next reply other threads:[~2019-10-22 17:13 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-22 17:12 David Hildenbrand [this message]
2019-10-22 17:12 ` [PATCH RFC v1 01/12] mm/memory_hotplug: Don't allow to online/offline memory blocks with holes David Hildenbrand
2019-10-24 3:53 ` Anshuman Khandual
2019-10-24 7:55 ` David Hildenbrand
2019-10-22 17:12 ` [PATCH RFC v1 02/12] mm/usercopy.c: Prepare check_page_span() for PG_reserved changes David Hildenbrand
2019-10-23 8:20 ` David Hildenbrand
2019-10-23 16:25 ` Kees Cook
2019-10-23 16:32 ` David Hildenbrand
2019-10-22 17:12 ` [PATCH RFC v1 03/12] KVM: x86/mmu: Prepare kvm_is_mmio_pfn() " David Hildenbrand
2019-10-22 17:12 ` [PATCH RFC v1 04/12] KVM: Prepare kvm_is_reserved_pfn() " David Hildenbrand
2019-10-22 17:12 ` [PATCH RFC v1 05/12] vfio/type1: Prepare is_invalid_reserved_pfn() " David Hildenbrand
2019-10-22 17:12 ` [PATCH RFC v1 06/12] staging/gasket: Prepare gasket_release_page() " David Hildenbrand
2019-10-23 8:17 ` David Hildenbrand
2019-10-22 17:12 ` [PATCH RFC v1 07/12] staging: kpc2000: Prepare transfer_complete_cb() " David Hildenbrand
2019-10-22 17:55 ` Matt Sickler
2019-10-22 21:01 ` David Hildenbrand
2019-10-22 17:12 ` [PATCH RFC v1 08/12] powerpc/book3s: Prepare kvmppc_book3s_instantiate_page() " David Hildenbrand
2019-10-22 17:12 ` [PATCH RFC v1 09/12] powerpc/64s: Prepare hash_page_do_lazy_icache() " David Hildenbrand
2019-10-22 17:12 ` [PATCH RFC v1 10/12] powerpc/mm: Prepare maybe_pte_to_page() " David Hildenbrand
2019-10-22 17:12 ` [PATCH RFC v1 11/12] x86/mm: Prepare __ioremap_check_ram() " David Hildenbrand
2019-10-22 17:12 ` [PATCH RFC v1 12/12] mm/memory_hotplug: Don't mark pages PG_reserved when initializing the memmap David Hildenbrand
2019-10-22 21:54 ` [PATCH RFC v1 00/12] mm: Don't mark hotplugged pages PG_reserved (including ZONE_DEVICE) Dan Williams
2019-10-23 7:26 ` David Hildenbrand
2019-10-23 17:09 ` Dan Williams
2019-10-23 17:27 ` David Hildenbrand
2019-10-23 19:39 ` Dan Williams
2019-10-23 21:22 ` David Hildenbrand
2019-10-24 12:50 ` David Hildenbrand
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